x86: implement CPUID 15h support #1189

Job	Run time
build-minimal-sysroots (x86_64)	1m 15s
build-minimal-sysroots (riscv64)	1m 45s
build-minimal-sysroots (arm64)	1m 5s
build-toolchains (ubuntu-latest, x86_64, gnu)	41s
build-toolchains (ubuntu-latest, riscv64, gnu)	55s
build-toolchains (ubuntu-latest, arm64, gnu)	30s
build-toolchains (ubuntu-20.04, x86_64, gnu)	1m 12s
build-toolchains (ubuntu-20.04, riscv64, gnu)	1m 26s
build-toolchains (ubuntu-20.04, arm64, gnu)	1m 19s
build-toolchains (ubuntu-latest, llvm, all)	1m 1s
build-llvm	3m 30s
build-riscv	3m 25s
build-llvm-riscv64	2m 59s
build	3m 18s
build-arm64	0s
build-llvm-arm64	0s
run-riscv	0s
run-riscv64-llvm	0s
run-x86_64-llvm	0s
run-x86_64	0s
	24m 21s

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